The invention is directed to the field of optical multiplexing and more specifically to linear arrays of integrated quantum well lasers for wavelength division multiplexing.
In the prior art there has been described wavelength division (frequency) multiplexing using several different methods for obtaining a number of differing but closely spaced optical wavelengths. An article by Aiki, Nakamura and Umeda, "A Frequency Multiplexing Light Source with Monolithically Integrated Distributed-Feedback Diode Lasers" IEEE Jr.of Quan.Elect., Vol.QE-13, No. 4, April 1977, P220-223, describes a light source consisting of a plurality of GaAs-AlGaAs distributed-feedback (DFB) diode lasers with different grating periods so that the lasers lase with different wavelengths having a separation of about 20 .ANG.. One major disadvantage to this approach is that the difference in the gratings causes many of the lasers to emit at wavelengths other than at the peak of their gain curve. Therefore, the lasing threshold current changes from laser-to-laser. An article by Alferov et al, "Wavelength Multiplexing DH AlGaAs Injection Laser Source with a Graded Composition Along the Active Layer", Jr.of Quan.Elect., Vol.QE-17, No. 8, August 1981, P1530-33, describes the use of DH AlGaAs wafers with graded composition along the active layer for creation of multiwavelength laser source for wavelength division multiplexing. An article by Tsang, "CW Multiwavelength Transverse Junction Stripe Lasers Grown by Molecular Beam Epitaxy Operating Predominantly in Single-Longitudinal Modes", Appl.Phys.Letters 36(6), Mar. 15, 1980, P441-3, describes a new transverse junction stripe laser structure with multiple active layers each emitting a different wavelength. This is not true WDM because all wavelengths will contain the same data.
In the present invention an integrated quantum well laser array for wavelength division multiplexing is described having many lasers per output channel all grown on the same substrate and wherein a controlled variation of the active layer thickness from one of the plurality of lasers to the next is used to provide lasers of different wavelengths.